Project Summary Antimicrobial neutrophils are immediate responders to bacterial infection and tissue damage. A large family of arachidonic acid (AA)-derived lipids, collectively termed eicosanoids, are crucial regulators of this response. Many eicosanoids are generated by oxidation of AA by 5-lipoxygenase (5-LO) and comprise some of the most potent leukocyte chemoattractants known in vertebrates, such as leukotriene B4. Leukotrienes have been intensely studied for decades, which led to the development of many successful anti-inflammatory drugs. Importantly, AA can be alternatively metabolized by 5-LO into another type of powerful chemotactic lipid, 5-oxo- ETE (5-oETE)?especially upon oxidative stress. 5-oETE signals through a specific G-protein coupled receptor, OXER1, that possesses identifiable orthologs in most vertebrates except rodents, rabbits, birds, and reptiles. Because mice, the predominant biomedical animal model, do not possess OXER1, the physiological functions of this pathway have remained virtually unstudied. Our published and preliminary data in zebrafish larvae?a powerful model for innate immunity in which OXER1 orthologues are expressed?suggest that 5-oETE acts as initial tissue damage signal, and that tissue damage signaling is essential for neutrophils to be able to detect bacterial infections in vivo. Thus, I hypothesize that 5-oETE attracts neutrophils to infection sites, paralleling the known physiological role of leukotrienes. Studying this neglected pathway could give rise to anti-inflammatory drugs that mirror the success of leukotriene antagonists. We will elucidate the role of 5-oETE by pharmacological and genetic perturbation in a zebrafish ear-infection assay, and develop novel fluorescence reporter tools to visualize 5-oETE release and signaling in cells and live animals. This research will pave way for understanding the physiological functions of this neglected inflammatory signaling pathway, and create novel imaging tools to study its pharmacology and biology in vitro and in vivo.